The present invention relates to an adhesive for semiconductor parts, and more particularly to an adhesive for semiconductor parts, which comprises a cyclic structure-containing thermoplastic polymer as a base polymer and has excellent shelf stability, adhesive property, heat resistance, moisture resistance, low water absorption property, dielectric properties (low dielectric constant and dielectric loss tangent), productivity, mechanical properties and long-term reliability. The present invention also relates to a production process of a semiconductor part package, comprising the step of bonding a semiconductor part to a wiring board (substrate) with such an adhesive. The present invention further relates to a semiconductor part package bonded with such an adhesive.
With the rapid advancement of advanced information-oriented society in recent years, there is a strong demand for the enhancement of throughput capacity of information processing apparatus such as computers and communication apparatus, i.e., the speeding up. In addition, their miniaturization and weight saving are required so as to be portable.
Of these requirements, in order to achieve the speeding up of the information processing, it is effective to make the interconnected wiring of passive parts and active parts such as LSI, memory and so as short as possible so as to make wiring density high in packaging of semiconductor parts mounted in an apparatus. This technique is also effective for the miniaturization and weight saving of information processing apparatus.
As a means for shortening the distance of the interconnected wiring, there is bare chip mounting in which semiconductor chips are directly mounted on a substrate. In particular, flip chip bonding (FC) in which an electrode of a semiconductor chip (semiconductor integrated circuit device) and an electrode of a wiring board are directly bonded to each other through bumps (fine metal projections; for example, Au bumps or solder bumps) is the most effective process.
In the flip chip bonding, metallurgical bonding making good use of a metallic material such as an Snxe2x80x94Pb solder has been mainly used. More specifically, when a semiconductor chip is mounted on a wiring board, the semiconductor chip is placed on a conductive pattern of the wiring board to conduct solder bonding. In the soldering process, it is necessary to conduct flow soldering subsequently to reflow soldering. Therefore, the process is complicated, and any part poor in heat resistance cannot be mounted. In addition, since joints in the adhesion or bonding of semiconductor parts are increasingly made small, the processing by the solder bonding becomes difficult.
In order to meet requirements such as high-density packaging and miniaturization of electronic apparatus, enhancement of electrical performance, reduction in production cost and automization of packaging, various surface mounting techniques including non-metallurgical bonding have therefore been developed. For example, a method, in which bumps are formed on a semiconductor chip, an insulating resin layer is formed on a wiring board, and both semiconductor chip and wiring board are headed and press-bonded to each other, thereby directly bonding an electrode of the semiconductor chip to an electrode of the wiring board in a shortest distance through bumps, is put to practical use. The insulating resin layer is generally formed by a thermosetting resin having adhesive property, such as an epoxy resin, and so adhesion between the semiconductor chip and the wiring board by the setting of the resin is conducted at the same time as the bonding between the electrodes.
Besides, a method, in which bumps are formed on a semiconductor chip, an anisotropic conductive film is interposed in a space between the semiconductor chip and a conductive pattern on a wiring board, and both chip and board are pressed against each other, thereby press-bonding the bumps of the semiconductor chip to the conductive pattern on the wiring board to form electrical connection, has been developed. The anisotropic conductive layer is generally formed by an anisotropic conductive material obtained by dispersing a conductive filler such as metallic fine particles or resin balls (fine particles), on the surfaces of which a conductive film has been provided, in a binder resin. In the bonding mechanism making use of the anisotropic conductive material, the conductive filler dispersed in the anisotropic conductive material is present on connection terminals with a certain probability, and the conductive filler is squeezed from point contact to a state close to face contact by applying heat and pressure upon bonding, thereby giving conductivity and at the same time fully bonding the chip to the wiring board to achieve stable bonding. If the filling amount of the conductive filler is too great, interterminal leakage and lowering of adhesive force are incurred. If the amount is too small on the other hand, a problem arises on connection resistance. More specifically, lateral insulation property and conductivity between upper and lower terminals are balanced by controlling the amount of the conductive filler dispersed. In addition, the adhesive force is controlled.
The non-metallurgical bonding using the insulating resin or anisotropic conductive material has a merit that the bonding can be conducted at a relatively low temperature compared with the solder bonding. According to the packaging by the non-metallurgical bonding, the limitation of materials to be bonded is relaxed compared with the solder bonding, and application range thereof is widened. The requirement of heat resistance to the parts and boards (substrates) can also be relaxed due to bonding at a lower temperature, and moreover packaging cost can be reduced because washing-out of flux is unnecessary.
In the non-metallurgical bonding, thermosetting resins and ultraviolet-curing resins have heretofore been commonly used as the insulating resins or binder resins from the viewpoints of adhesive property and heat resistance. However, the bonding using the thermosetting resin or ultraviolet-curing resin has involved a problem of repairability against bonding failure occurred in a packaging process. More specifically, it is extremely difficult to repair a defective unit when such a resin is cured by heating and pressing (pressurizing) or irradiation of ultraviolet light upon bonding. Even if a semiconductor chip can be separated from a wiring board, it is difficult to remove residue of the cured resin. In the case of a semiconductor package, to scrap the whole package due to a partial defect results in a great loss of cost. Accordingly, there is a demand for establishing techniques such as repair of wiring, and exchange and reuse of semiconductor chips.
In these application fields, thermosetting epoxy resins (adhesives) have heretofore been particularly preferably used because variations of its connection resistance value under high-temperature conditions are little. The epoxy resins are roughly divided into one-pack type that a main material is mixed with a hardener in advance, and two-pack type that a main material is mixed with a hardener upon use. However, in the case of the one-pack type epoxy resins in which the main material is mixed with the hardener in advance, most of them must be stored under refrigeration in order to prevent the reaction of the main material with the hardener before use. Since the one-pack type epoxy resins are cured at a low temperature, their pot life at room temperature is at most about 1 day. Even when they are stored under refrigeration, the pot life is about 2 to 3 months. In addition, their workability is poor because the temperature must be returned to room temperature upon use. Further, the one-pack type epoxy resins involve a problem that they take up moisture when the temperature is returned to room temperature to deteriorate their properties.
On the other hand, in the case where that the two-pack type epoxy resins in which the main material is mixed with the hardener upon use, there is a problem that their workability is poor because the main material must be mixed with the hardener at every use. In the joining and adhesive bonding with such an adhesive, a coating technique for quickly and exactly applying the adhesive is important for the purpose of joining or adhesive bonding many parts in a short period of time. A screen printing method or an ejection method by a dispenser is generally applied. Occurrence of coat mottle becomes a problem when these methods are applied. The two-pack type epoxy resins are difficult to control their coating weights and hence involve a problem that coating mottle tends to occur, and stable adhesion is infeasible.
As the common problem before the one-pack type and two-pack type epoxy resins, there is a problem that it takes a long time to cure them, namely, the productivity is low. In addition, the insulating resin or anisotropic conductive material may be required in some cases to be used in the form of a film or sheet, and the epoxy resin is required to be partially cured so as to become tack-free when a sheet is formed therefrom. Such partial curing is difficult to control, and moreover a problem arises on the stability and shelf stability of the resulting sheet.
In addition, the epoxy resins are insufficient in adhesive property and mechanical strength and poor in moisture resistance, dielectric properties and low impurity absorption property, and further offer problems on dielectric properties at a high temperature and changes thereof with time. It is accordingly difficult for the epoxy resins to achieve stability and high reliability at high temperature and high humidity. Further, movable ions in the resins may adversely affect semiconductor parts in some cases.
In recent years, attention has been paid to thermoplastic norbornene resins having a repeating unit derived from a cycloolefin as resin materials excellent in heat resistance, moisture resistance, electric properties and low impurity absorption property. For example, Japanese Patent Application Laid-Open No. 27412/1987 discloses modified cycloolefin copolymers obtained by graft-modifying a cycloolefin copolymer such as an addition polymer of tetracyclododecene and ethylene with allyl glycidyl ether or maleic anhydride. However, it has not been proposed to use such thermoplastic norbornene resins as adhesives in mounting of semiconductor parts.
It is an object of the present invention to provide an adhesive for semiconductor parts, which is excellent in shelf stability, adhesive property, heat resistance, moisture resistance, low water absorption property, dielectric properties, productivity, mechanical properties and long-term reliability.
Another object of the present invention is to provide a process for producing a semiconductor part package, comprising the step of bonding a semiconductor part to a wiring board with such an adhesive excellent in various properties.
A further object of the present invention is to provide a semiconductor package bonded with such an adhesive excellent in various properties.
The present inventors have carried out an extensive investigation with a view toward overcoming the above-described problems involved in the prior art. As a result, it has been found that at least one cyclic structure-containing thermoplastic polymer selected from the group consisting of (a) a cycloolefin polymer and (b) an aromatic-condensed polymer having a repeating unit of an aromatic ring in its main chain, and having a number average molecular weight of 1,000 to 500,000 is used as base polymer, whereby an adhesive for semiconductor parts, which is excellent in the above-described various properties, can be obtained.
The cyclic structure-containing thermoplastic polymer useful in the practice of the present invention desirably has a functional group, particularly a polar group in order to improve its adhesion to metals, other resins and the like.
The adhesive according to the present invention is generally used in the form of an adhesive solution or adhesive film (including a sheet). A filler may be contained in the adhesive according to the present invention, thereby controlling the coefficient of linear expansion thereof within a desired range, and moreover enhancing the strength of a film formed from such an adhesive, and consequently also enhancing the adhesive strength. The adhesive according to the present invention can also be provided as an anisotropic conductive material by containing a conductive filler therein. Further, a low-molecular weight component such as an epoxy resin or petroleum resin may be contained in the adhesive according to the present invention, thereby controlling the viscosity thereof within a desired range and moreover enhancing the adhesive property to semiconductor parts and boards (substrates) having fine irregularities. The adhesive according to the present invention can satisfy evaluation criteria according to a temperature cycle test and a high-temperature and high-humidity test.
The adhesive according to the present invention is an adhesive comprising a.cyclic structure-containing thermoplastic polymer as a base polymer and has excellent repairability because no hardener is used. Besides, the adhesive according to the present invention is excellent in shelf stability because no hardener is used, and in productivity because the time required for curing is unnecessary. More specifically, the adhesive according to the present invention can be bonded by heating and melting it to and then cooling it, or applying an organic solvent solution thereof and then drying it.
According to the present invention, there is thus provided an adhesive for semiconductor parts, comprising, as a base polymer, at least one cyclic structure-containing thermoplastic polymer selected from the group consisting of (a) a cycloolefin polymer and (b) an aromatic-condensed polymer having a repeating unit of an aromatic ring in its main chain, and having a number average molecular weight of 1,000 to 500,000.
According to the present invention, there is also provided an adhesive film for semiconductor parts, which is obtained by forming a film from the above-described adhesive.
According to the present invention, there is further provided a semiconductor part package obtained by bonding a semiconductor part to a substrate with a solution or film of the above-described adhesive.
According to the present invention, there is still further provided a process for producing a semiconductor part package, which comprises laminating the above-described adhesive film on the surface of a substrate, placing a semiconductor part on the adhesive film, bonding the semiconductor part to the substrate by heating and pressurizing the adhesive film at a temperature not lower than the glass transition temperature of the cyclic structure-containing thermoplastic polymer, and then cooling the adhesive film.
According to the present invention, there is yet still further provided a process for producing a semiconductor part package, which comprises applying a solution of the above-described adhesive to the surface of a substrate, drying a solvent to form an adhesive layer, placing a semiconductor part on the adhesive layer, bonding the semiconductor part to the substrate by heating and pressurizing the adhesive layer at a temperature not lower than the glass transition temperature of the cyclic structure-containing thermoplastic polymer. and then cooling the adhesive layer.